In the last several years, prophylactic knee braces have been widely marketed as a means for reducing the high incidence of serious ligament injuries occurring in football and other sports. However, no scientific consensus yet establishes the efficacy of these devices. Field trails and laboratory experiments provide complementary information needed to resolve this issue. However, even if it can be proven that current knee braces are of some benefits, the empirical nature of their designs makes it unlikely that such devices are optimal. In fact, preliminary evidence from our laboratory and in the literature suggests distinctly different performance characteristics between existing braces. We suspect that prophylactic knee brace performance is sensitive to one more major design variables, and that these design variables can be most efficiently identified in a well- controlled laboartory model. We propose series of parametric laboratory trials to document how the degree of afforded ligament protection varies in accordance with realistic changes in the major design variables. We will pursue two specific aims. First, we will refine and further validate an existing laboratory surrogate knee model which has proven useful for comparative studies of several commerical braces. This surrogate knee model incorporates modularly-replaceable polymeric ligament analogs whose mechanical properties (stiffness and strength) approximate those of normal human ligaments; we have completed initial validation against cadaveric performance under dynamic valgus loading conditions. The surrogate model overcomes many of the difficulties inherent in cadaver material as a vehicle for brace testing. Our second specific aim is to use this surrogate model to document failure load changes and ligament strain changes accompanying parametric changes in the major design variables that characterize prophylactic knee braces. These parametric design variations are to be efficiently achieved by means of interchangeable component substitutions in a modular, five-piece generic knee brace model.